Description of Heterodiniaceae

Gonyaulacid dinoflagellates, dorso-ventrally flatened, the cell is slightly asymmetrical; sulcus midventral; usually 2 well defined antapical horns; a postcingular horn may be present. Tabulation: 6 precingular plates; 6 postcingular plates; 4 large climactal plates (3 apical and a left lateral anterior intercalary); ventral pore situated on a small platelet set in a depressed pit on the ventral epicone.